CARBON COMPOUNDS PART-2

Properties of covalent bond

  • Covalent compounds are formed by the sharing of electrons between atoms.
  • They are generally soluble in organic solvents like alcohol, ether, or carbon tetrachloride.
  • Their melting and boiling points are low.
  • These are soft, easily fusible, and volatile.
  • A covalent bond has directional properties.

 

Three Kinds of Covalent Bonds of Carbon-

Single bonds

  • Single bond simply means sharing one pair of bonding electrons between two atoms and is represented by a single line.

Double bonds

  • In a double bond, two pairs of electrons are shared.

Triple bonds

  • In a triple bond, three pairs of electrons are shared

Polar and non-polar covalent bond-

  • Depending on the electron affinity or electronegativity (tendency of atoms to attract electrons), the shared pair of electrons may be equally or unequally shared.
  • The binary homonuclear covalent molecule has to be nonpolar. Since the bonding elements possess the same electronegativity. In such cases, the bonding electrons are shared equally by two atoms.
  • Heteronuclear polar diatomic molecules are polar due to differences in their electronegativities.

 

Polar Covalent Bond

Non-Polar Covalent Bond

Hydrogen Fluoride (HF)

Nitrogen (N2)

Ozone (O3)

Methane (CH4)

Ammonia (NH3)

Carbon Dioxide (CO2)

Hydrogen Sulfide (H2S)

Chlorine (Cl2)

 

Isotopes of carbon :

  • Carbon - 12 (12C) - contains six neutrons and six protons. 
  • Carbon - 13 (13C) - has seven neutrons and six protons. 
  • Both 12C and 13C are called stable isotopes since they do not decay into other forms or elements over time. 
  • The rare carbon -14 (14C) isotope contains eight neutrons in its nucleus. It is unstable, or radioactive. 
  • Over time, a 14C atom will decay into a stable product.

  • The vast majority of all carbon found on Earth is 12C. 
  • Almost 99% of all carbon on Earth is of C - 12.
  • While only approximately 1% of all carbon on Earth is of the 13C isotopic form, 14C is still much rarer. 

 

AllotropyThe phenomenon in which the element exists in two or more different physical states with similar chemical properties are called Allotropy.

Allotropes of Carbon

Diamond

  • It has a crystalline lattice. 
  • In diamond each carbon atom undergoessp3 hybridisation and linked to four other carbon atoms by using hybridised orbitals in tetrahedral fashion. 
  • The C–C bond length is 154 pm. 
  • The structure extends in space and produces a rigid three dimensional network of carbon atoms.  It is very difficult to break extended covalent bonding and, therefore, diamond is a hardest substance on the earth. 
  • It is chemically inert.
  • It is bad conductor of heat and electricity.
  • Diamond has very high refractive index.
  • It is a colourless and shining solid.
  • It has high melting point.

Uses :

  • It is used as an abrasive for sharpening hard tools, in making dyes and in the manufacture of tungsten filaments for electric light bulbs.
  • It is used in jewellery as a precious stone.
  • It is used for cutting glass, making bores for rock drilling and for making abrasives.
  • It is also used for making dies for drawing thin wires from metals.

Graphite-

  • Graphite is the allotrope of carbon.
  • It is chemically more reactive than diamond.
  • Due to presence of free electrons, it is a good conductor of electricity.
  • Graphite is thermodynamically more stable than diamond.
  • It is soft and has a hexagonal planar structure.
  • Layers are held by van der Waals forces and distance between two layers is 340 pm. 
  • Each layer is composed of planar hexagonal rings of carbon atoms. C—C bond length within the layer is 141.5 pm. 
  • Each carbon atom in hexagonal ring undergoes sp2 hybridisation and makes three sigma bonds with three neighbouring carbon atoms. Fourth electron forms a π bond. The electrons are delocalised over the whole sheet. 

 

Uses 

  • It is used in making lead pencils 
  • It is used as lubricant in machinery
  • It is used as  a moderator in nuclear reactor
  • It is used for lining and making electrodes.

Fullerene-

  • They are also called Bucky balls.
  • Buckminster fullerene, C60 has soccer ball shape structure with 12 pentagons and 20 hexagon rings of carbon atoms.
  • C70 has rugby ball shape structure.
  • In fullerene each carbon atom is sp2 hybridized.
  • Fullerenes are made by the heating of graphite in an electric arc in the presence of inert gases such as helium or argon. 
  • It is used as insulators, used as a catalyst in the water purification.

 

 

Versatile Nature of Carbon

The two characteristic properties of carbon element which lead to the formation of large number of compounds -

Catenation – Carbon can link with carbon atoms by means of covalent bonds to form long chains, branched chains and closed ring compound. Carbon atoms may be linked by single, double or triple bonds.

This property is due to

  • The small size of the carbon atom.
  • The great strength of the carbon-carbon bond.

Tetravalency – Carbon has 4 valence electrons. Carbon can bond with four carbon atoms, monovalent atoms, oxygen, nitrogen and sulphur.

Hydrocarbons- Those compounds which contain or have only carbon and hydrogen atoms are known as hydrocarbons

Saturated hydrocarbon

Unsaturated hydrocarbon

Hydrocarbons having single bonds between carbon atoms are called saturated hydrocarbons.

Hydrocarbons having double or triple multiple bonds between carbon atoms are called unsaturated hydrocarbons

They are less reactive.

They are highly reactive.

They include alkanes and cycloalkanes.

They include alkenes , alkynes and aromatic compounds.

Gives a clean flame on burning.

They give yellow flame with a lot of black smoke on burning.

 

Alkane :

  • Hydrocarbons containing a single bond between carbon atoms are known as alkanes.
  • General formula : CnH2n+2 (+ane suffix)
  • They are also known as paraffin.
  • Example : Methane , Ethane , Propane etc.

Alkenes :

  • Hydrocarbons containing a double bond between carbon atoms are known as alkenes.
  • General formula : CnH2n (+ ene suffix).
  • They are also known as olefins.

Alkynes :

  • Alkynes are unsaturated hydrocarbons.
  • They contain at least one triple bond between two carbon atoms.
  • General formula is CnH2n–2 (+ yne suffix).